You be assumin right. You can use the 16 in the 12 ga events in skeet. 12 ga used to be called all bore cause you can use any in that event. I commonly use the 20 ga in the 12 ga event and I am not alone. There were lots of 16 ga M-12s made to shoot skeet. I even had a 5 gun skeet set made by the factory for an old skeet shooter. 12..16--20--28 ga and a M-42 410. The 16 ga commonly shot an ounce of shot in skeet loads while the 12 shot and ounce and an eighth. I have a lady friend who shoots skeet and all she shoots is the 28 ga and the 410. She shoots the 28 in all the other gauges and the 410 in the 410 events. She is very small and doesn't care for recoil.
Now go shoot and have fun!